The monthly security release window for Drupal 8 and 7 core will take place on Wednesday, August 16.

This does not mean that a Drupal core security release will necessarily take place on that date for any of the Drupal 8 or 7 branches, only that you should watch for one (and be ready to update your Drupal sites in the event that the Drupal security team decides to make a release).

Drupal 8.4.0-beta1 will also be released sometime during the week to continue preparation for the upcoming minor release in October.

There will be no bug fix or stable feature release on this date. The next window for a Drupal core patch (bug fix) release for all branches is Wednesday, September 06. The next scheduled minor (feature) release for Drupal 8 will be on Wednesday, October 5.